Import MultiScaleDeformableAttention in ops __init__ for registry

The shim's __init__.py must import the multi_scale_deform_attn
module so that @ATTENTION .register_module() is executed at import
time, making it available in the attention registry.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

setup_mmcv_shim.py

@@ -128,6 +128,12 @@ def deform_conv2d(*args, **kwargs):
 
 def get_onnxruntime_op_path():
     return ""
+
+# Import multi_scale_deform_attn to trigger ATTENTION registry registration
+try:
+    from mmcv.ops.multi_scale_deform_attn import MultiScaleDeformableAttention as _MSDA
+except Exception:
+    pass
 '''
 
 with open(os.path.join(ops_dir, '__init__.py'), 'w') as f: